Techniques for constraint flag signaling for range extension with coding for last significant coefficient

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video data processing. In some examples, an apparatus for video data processing includes processing circuitry. For example, the processing circuitry determines a first syntax element for coding control in a first scope of coded video data in a bitstream. The first syntax element is associated with a coding tool for coding a position of a last significant coefficient during an entropy coding of transform coefficients. Then, in response to the first syntax element being a first value indicative of disabling of the coding tool in the first scope, the processing circuitry decodes the first scope of coded video data in the bitstream that includes one or more second scopes of coded video data without invoking the coding tool.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 63/250,155, “TECHNIQUES FOR CONSTRAINT FLAGSIGNALING FOR RANGE EXTENSION WITH REVERSE LAST SIGNIFICANT COEFFICIENT”filed on Sep. 29, 2021. The entire disclosure of the prior applicationis hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has specific bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine differentdirections could be represented. That increased to 33 in H.265 (year2013), and JEM/VVC/BMS, at the time of disclosure, can support up to 65directions. Experiments have been conducted to identify the most likelydirections, and certain techniques in the entropy coding are used torepresent those likely directions in a small number of bits, accepting acertain penalty for less likely directions. Further, the directionsthemselves can sometimes be predicted from neighboring directions usedin neighboring, already decoded, blocks.

FIG. 1B shows a schematic (180) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for video dataprocessing. In some examples, an apparatus for video data processingincludes processing circuitry. For example, the processing circuitrydetermines a first syntax element for coding control in a first scope ofcoded video data in a bitstream. The first syntax element is associatedwith a coding tool for coding a position of a last significantcoefficient during an entropy coding of transform coefficients. Then, inresponse to the first syntax element being a first value indicative ofdisabling of the coding tool in the first scope, the processingcircuitry decodes the first scope of coded video data in the bitstreamthat includes one or more second scopes of coded video data withoutinvoking the coding tool.

In some embodiments, the first syntax element is in general constraintinformation for coding control of pictures in an output layer set. Thefirst value of the first syntax element is indicative of disabling thecoding tool in each coded layer video sequence (CLVS) in the outputlayer set. The coding tool codes a position of a last significantcoefficient in a transform block relative to a bottom right corner ofthe transform block. In some examples, the processing circuitryconstrains a second syntax element for coding control of a coded layervideo sequence (CLVS) in the bitstream to have a value indicative of noinvoking of the coding tool for decoding the CLVS. In an example, thevalue of the second syntax element indicates a nonexistence of a sliceheader flag associated with the coding tool in a slice header of a slicein a picture of the CLVS.

In some embodiments, in response to the first syntax element being asecond value, the processing circuitry determines a value of a secondsyntax element for coding control of a coded layer video sequence (CLVS)in the bitstream. The second syntax element is indicative of anenabling/disabling of the coding tool in the CLVS. Further, in someexamples, in response to the value of the second syntax elementindicative of an enabling of the coding tool in the CLVS, the processingcircuitry decodes a slice header flag in a slice header of a slice, theslice header flag is indicative of a use/no use of the coding tool forcoding the slice.

In some embodiments, to determine the value of the second syntaxelement, the processing circuitry infers, in response to the secondsyntax element not presenting in a sequence parameter set (SPS) for theCLVS, the value of the second syntax element for indicating a disable ofthe coding tool in the CLVS.

In some embodiments, to determine the first syntax element, theprocessing circuitry decodes the first syntax element from a syntaxstructure for general constraint information in response to a syntaxelement in the syntax structure indicating additional bits for generalconstraint information in the syntax structure.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the methodsfor video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows examples for signaling adaptive resolution change (ARC)parameters according to embodiments of the disclosure.

FIG. 10 shows an example of a Table (1000) for mapping of upsample ordownsample factors, codewords, and Ext-Golomb codes.

FIG. 11 shows some examples of ARC parameters signaling according tosome embodiments of the disclosure.

FIG. 12 shows a syntax structure example of a set of PTL syntax elementsin some examples.

FIG. 13 shows a syntax structure example of general constraintinformation in some examples.

FIGS. 14A-14B show examples of PTL information that includes a PTLsyntax structure and a general constraint information syntax structureaccording to some embodiments of the disclosure.

FIGS. 15A-15B show an example of a general constraint information syntaxstructure according to an embodiment of the disclosure.

FIG. 16 shows a syntax structure of general constraint informationaccording to some embodiments of the disclosure.

FIG. 17 shows a syntax structure example of sequence parameter set (SPS)range extension according to some embodiments of the disclosure.

FIG. 18 shows a flow chart outlining a process according to anembodiment of the disclosure.

FIG. 19 shows a flow chart outlining a process according to anembodiment of the disclosure.

FIG. 20 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide control techniques of coding tool(s)and functionalities with constraint flags in a coded video stream.

According to an aspect of the disclosure, picture size in a bitstreammay stay the same or may change. In some related examples, videoencoders and decoders can operate on a given picture size that isdefined and remains constant for a coded video sequence (CVS), a groupof pictures (GOP), or a similar multi-picture timeframe. In an example,such as in MPEG-2, system designs are known to change a horizontalresolution (and thus a picture size) dependent on factors such asactivity of a scene, but only at I pictures, hence picture size isdefined and remains constant typically for a GOP. Resampling ofreference pictures for use of different resolutions within a CVS isknown, for example, from ITU-T Rec. H.263 Annex P. However, the picturesize in the CVS does not change, only the reference pictures areresampled, resulting potentially in only parts of a picture canvas beingused (e.g., in the case of down-sampling), or only parts of a scenebeing captured (e.g., in the case of up-sampling). In some examples,such as in H.263 Annex Q, resampling of an individual macroblock by afactor of two in each dimension (e.g., upward or downward) is allowed.However, the picture size remains the same. When the size of themacroblock can be fixed, for example, in H.263, and thus the size of themacroblock does not need to be signaled.

In some related examples, a picture size in predicted pictures can bechanged. In an example, such as VP9, reference picture resampling andchanging of a resolution for a whole picture are allowed. In someexamples (for example, Hendry, et. al, “On adaptive resolution change(ARC) for VVC”, Joint Video Team document JVET-M0135-v1, Jan. 9-19,2019, which are incorporated herein in their entireties), resampling ofa whole reference picture to a different resolution (e.g., a higherresolution or a lower resolution) is allowed. Different candidateresolutions can be coded in a sequence parameter set (SPS) and can bereferred to by per-picture syntax elements in a picture parameter set(PPS).

According to an aspect of the disclosure, a source video can becompressed by layered coding that can encode pictures into a bitstreamthat includes one or more layers with different qualities, such asdifferent resolutions. The bitstream can have syntax elements thatspecify which layer(s) (or a set of layers) can be output at a decoderside. The set of layers to be output can be defined as an output layerset. For example, in a video codec that supports multiple layers andscalabilities, one or more output layer sets can be signaled in a videoparameter set (VPS). Syntax elements specifying profile tier level (PTL)for the entire bitstream or one or more output layer sets can besignaled in a VPS, a decoder parameter set (DPS) that may be referred toas decoder capability information (DCI) in some examples, a SPS, a PPS,a SEI message, or the like. In the PTL information, general constraintinformation that can specify constraints on coding tools orfunctionalities can be present. It is desirable to efficiently representand signal constraint information for various coding tools andfunctionalities.

In some examples, a term “sub-picture” can be used to refer to, forexample, a rectangular arrangement of samples, blocks, macroblocks,coding units, or similar entities that is semantically grouped and maybe independently coded in changed resolution. One or more sub-picturescan form a picture. One or more coded sub-pictures can form a codedpicture. One or more sub-pictures can be assembled into a picture, andone or more sub pictures can be extracted from a picture. In someexamples, one or more coded sub-pictures can be assembled in acompressed domain without transcoding to a sample level into a codedpicture. In some examples, one or more coded sub-pictures can beextracted from a coded picture in the compressed domain.

In some examples, mechanisms that allow a change of a resolution of apicture or a sub-picture in a CVS by, for example, reference pictureresampling can be referred to as adaptive resolution change (ARC).Control information used to perform adaptive resolution change can bereferred to as ARC parameters. The ARC parameters can include filterparameters, scaling factors, resolutions of an output and/or a referencepicture, various control flags, and/or the like.

In some examples, encoding/decoding of ARC is in the unit of a picture,thus a set of control information (ARC parameters) is used for theencoding/decoding a single and semantically independent coded videopicture. In some examples, encoding/decoding of ARC is in the unit of asub-picture, thus multiple sub-pictures in a picture can beencoded/decoded with independent ARC parameters. It is noted that ARCparameters can be signaled using various techniques.

FIG. 9 shows examples (e.g., options) of techniques for signaling ARCparameters according to some embodiments of the disclosure. Codingefficiency, complexity, and architecture can vary among the examples. Avideo coding standard or technology may choose one or more of theexamples, or other variations, for signaling ARC parameters. Theexamples may not be mutually exclusive, and may be interchanged based onapplication needs, standards technologies, choice of an encoder, and/orthe like.

According to an aspect of the disclosure, ARC parameters may be providedas classes of ARC parameters in various manners. In some examples, aclass of ARC parameters includes upsample and/or downsample factors,separate or combined in an X dimension and a Y dimension. In an example,one or more short syntax elements that can point to a table includingthe upsample and/or downsample factors can be coded.

In some examples, a class of ARC parameters includes upsample and/ordownsample factors, with an addition of a temporal dimension, indicatinga constant speed zoom in and/or out for a given number of pictures. Inan example, one or more short syntax elements that can point to a tableincluding the upsample and/or downsample factors with the addition ofthe temporal dimension can be coded.

In some examples, a class of ARC parameters includes a resolution, inthe X dimension or the Y dimension, in units of samples, blocks,macroblocks, CUs, or any other suitable granularity, of an inputpicture, an output picture, a reference picture, a coded picture,combined or separately. In some examples, there are more than oneresolution used in video coding (e.g., one resolution for the inputpicture, another resolution for the reference picture), a set of values(corresponding to one of the resolutions) can be inferred from anotherset of values (corresponding to another of the resolutions). Thedetermination of the values can be gated, for example, based on the useof flags. The usage of flags for gating which will be described indetail in further description.

In some examples, a class of ARC parameters includes warping coordinatesthat are similar to that used in the H.263 Annex P, in a suitablegranularity as described above. The H.263 Annex P defines an efficientway to code the warping coordinates. Other efficient ways can bedevised. For example, the variable length reversible, Huffman-stylecoding of warping coordinates of Annex P can be replaced by a suitablelength binary coding where the length of the binary code word can bederived from a maximum picture size that is multiplied by a factor andoffset by a value to allow for warping outside of boundaries of themaximum picture size.

In some examples, a class of ARC parameters includes upsample and/ordownsample filter parameters. In an example, there is only a singlefilter for upsampling and/or downsampling. In another example, multiplefilters can be used. In some examples, the filter parameters may besignaled to allow more flexibility in a filter design. The filterparameters can be selected by using an index in a list of possiblefilter designs. The filter may be fully specified (e.g., by specifying alist of filter coefficients, using suitable entropy coding techniques),the filter may be implicitly selected through upsample or downsampleratios which are signaled according to any of the mechanisms describedabove, and/or the like.

In the following description, a finite set of upsample or downsamplefactors (the same factor to be used in both the X dimension and the Ydimension) is used to illustrate signaling ARC parameters through acodeword. In some examples, the codeword can be variable length coded,for example, using an Ext-Golomb code for certain syntax elements invideo coding specifications (e.g., H.264 and H.265).

FIG. 10 shows an example of a Table (1000) for mapping of upsample ordownsample factors, codewords, and Ext-Golomb codes.

It is noted that other similar mappings can be devised according to anapplication and capabilities of upscale and downscale mechanismsavailable in a video compression technology or standard. In someexamples, Table 1 can be suitably extended to additional values. It isnoted that values may be represented by entropy coding mechanisms otherthan the Ext-Golomb code, for example, by using a binary coding. In anexample, entropy coding mechanisms other than the Ext-Golomb code mayhave certain advantages when the resampling factors are of interestoutside the video processing engines (e.g., an encoder and a decoder),for example, by media-aware network elements (MANEs). In some examples,when no resolution change is required (e.g., the original/targetresolution being 1 in Table 1), a short Ext-Golomb code (e.g., only asingle bit shown in Table 1) can be chosen, which can have a codingefficiency advantage, for example, over using binary codes for the mostcommon case.

According to an aspect of the disclosure, the mapping table, such asTable 1 can be configurable. For example, the number of entries in Table1, and corresponding semantics can be fully or partially configurable.In some examples, a basic outline of mapping table is conveyed in a highlevel parameter set, such as an SPS or a DPS. Alternatively or inaddition, in some examples, one or more tables similar to Table 1 may bedefined in a video coding technology or standard, and one of the tablesmay be selected through, for example, an SPS or a DPS.

The ARC information, such as an upsample or downsample factor coded asdescribed above, may be included in a video coding technology orstandard syntax. It is noted that one or more codewords can be used tocontrol other classes of ARC information, such as the upsample ordownsample filters. In some examples, a comparatively large amount ofdata is required for a filter or other data structures.

Referring to FIG. 9 , in an example (910), such as in H.263 Annex P, ARCinformation (912) can be in a form of four warping coordinates, and isincluded in a picture header (911), such as in an H.263 PLUSPTYPE (913)header extension. The example (910) can be applied when i) a pictureheader is available, and ii) frequent changes of the ARC information areexpected. However, the overhead when using the H.263-style signaling,such as shown in the example (910), can be high, and scaling factors maynot be applicable among picture boundaries as the picture header can beof a transient nature.

Referring to FIG. 9 , in an example (920), such as JVCET-M135-v1, ARCreference information (925) (e.g., an index) can be placed in a PPS(924) and can point to a table (or a target resolution table) (926)including target resolutions (e.g., resolutions 1-3). In an example, thetable (926) is located inside an SPS (927). Placing the targetresolutions in the table (926) in the SPS (927) can be justified byusing the SPS as an interoperability negotiation point during capabilityexchange. A resolution can change, within a limited set of the values(e.g., the resolutions 1-3) in the table (926) from one picture toanother picture by the referencing (e.g., ARC reference information(925)) in the appropriate PPS (924).

FIG. 9 also shows additional techniques, such as examples (930), (940)and (950), that may be used to convey ARC information in a videobitstream. The techniques may be used individually or can be used insuitable combination, in a same video coding technology or standard.

Referring to FIG. 9 , in the example (930), ARC information (939), suchas a resampling factor (or zoom factor) may be present in a header, suchas a slice header, a GOB header, a tile header, a tile group header, orthe like. A tile group header (938) is illustrated in FIG. 9 forexample. The technique, illustrated by the example (930), can be usedwhen the ARC information (939) can be coded with a small number of bits,such as a single variable length ue(v) or a fixed length codeword of afew bits.

According to an aspect of the disclosure, having the ARC information(939) in a header (e.g., the tile group header (938) in FIG. 9 , a sliceheader, or a tile header) directly can have additional advantages inthat the ARC information (939) may be applicable to a sub-picturerepresented by, for example, a corresponding tile group (or a slice, atile), rather than an entire picture. In addition, in an example, evenif a video compression technology or standard envisions only wholepicture adaptive resolution changes (in contrast to, for example, a tilegroup based adaptive resolution changes), the example (930) can havecertain advantages over the example (910) from an error resilienceviewpoint.

Referring to FIG. 9 , in the example (940), ARC information (942) may bepresent in a parameter set (941), such as a PPS, a header parameter set,a tile parameter set, an adaptation parameter set (APS), or the like. AnAPS (941) is illustrated in FIG. 9 for example. In some examples, thescope of the parameter set (941) can be not larger than a picture, forexample, can be a picture, a tile group and the like. The use of the ARCinformation (e.g., the ARC information (942)) can be implicit throughthe activation of the relevant parameter set (e.g., the APS (941)). Forexample, when a video coding technology or standard contemplates onlypicture-based ARC, a PPS or equivalent may be appropriate.

Referring to FIG. 9 , in the example (950), ARC reference information(953) may be present in a tile group header (954) or a similar datastructure (e.g., a picture header, a slice header, a tile header, or aGOP header) as described above. The tile group header (954) isillustrated in FIG. 9 as an example. The ARC reference information (953)can refer to a subset of ARC information (955) available in a parameterset (956) with a scope beyond a single picture, for example an SPS, aDPS, or the like. The SPS (956) is illustrated in FIG. 9 as an example.

FIG. 11 shows some examples of ARC parameters signaling according tosome embodiments of the disclosure. FIG. 11 shows syntax diagramexamples used in video coding standards. In an example, the notation ofthe syntax diagrams roughly follows C-style programming. Lines inboldface can indicate syntax elements present in a bitstream, and lineswithout boldface can indicate control flow(s) or setting of variables.

Referring to FIG. 11 , a tile group header (1101) includes syntaxstructure of a header applicable to a part (e.g., a rectangular part) ofa picture. In an example, the tile group header (1101) can conditionallyinclude, a variable length, Exp-Golomb coded syntax elementdec_pic_size_idx (1102) (depicted in boldface). The presence of thesyntax element (e.g., the dec_pic_size_idx (1102)) in the tile groupheader (1101) can be gated based on an adaptive resolution, for example,represented by a flag (e.g., an adaptive_pic_resolution_change_flag)(1103). A value of the flag (e.g., theadaptive_pic_resolution_change_flag) (1103) is not depicted in boldface,and thus the flag is present in the bitstream at a point where the flagoccurs in the syntax diagram. Whether the adaptive resolution is in usefor the picture or the part of the picture can be signaled in a highlevel syntax structure (e.g., an SPS (1110) in FIG. 11 ) inside oroutside the bitstream.

Referring to FIG. 11 , an excerpt of an SPS (1110) is shown. The SPS(1110) includes a first syntax element (1111) that is a flag (1111)(e.g., an adaptive_pic_resolution_change_flag). When the flag (1111) istrue, the flag (1111) can indicate a use of the adaptive resolutionwhich may require certain control information. In an example, thecertain control information is conditionally present based on a value ofthe flag (1111) as shown by an if ( )statement (1112) in the SPS (1110)and the tile group header (1101).

When the adaptive resolution is in use, such as shown in the example inFIG. 11 , an output resolution in units of samples (or a resolution ofan output picture) (1113) can be coded. In an example, the outputresolution (1113) is coded based on a width resolution (e.g., anoutput_pic_width_in_luma_samples) and a height resolution (e.g., anoutput_pic_height_in_luma_samples). In a video coding technology orstandard, certain restrictions to value(s) of the output resolution(1113) can be defined. For example, a level definition may limit anumber of total output samples (e.g., a product of theoutput_pic_width_in_luma_samples and theoutput_pic_height_in_luma_samples). In some examples, a video codingtechnology or standard, or an external technology or standard (e.g., asystem standard) can limit a numbering range for the width resolutionand/or height resolution (e.g., the width resolution and/or the heightresolution are divisible by a power of 2), an aspect ratio of the widthresolution over the height resolution (e.g., a ratio of the widthresolution over the height resolution is 4:3 or 16:9), or the like. Inan example, the above restrictions may be introduced to facilitatehardware implementations.

In certain applications, an encoder can instruct a decoder to use acertain reference picture size rather than implicitly assume that a sizeis the output picture size. For example, a syntax element (e.g., areference_pic_size_present_flag) (1114) gates a conditional presence ofreference picture dimensions (1115). The reference picture dimensions(1115) can include, in an example, both a width (e.g., areference_pic_width_in_luma_samples) and a height (e.g., areference_pic_height_in_luma_samples).

Also in FIG. 11 , a table of applicable decoding picture widths andheights is illustrated. In an example, the number of entries in thetable can be expressed by a table indication (e.g., a syntax elementnum_dec_pic_size_in_luma_samples_minus1) (1116). The “minus1” can referto the interpretation of the value of the syntax element (1116). Forexample, if the coded value is zero, one table entry is present. If thecoded value is five, six table entries are present. For each entry inthe table, the decoded picture width and height are included as syntaxelements (1117).

The table entries represented by the syntax elements (1117) can beindexed using the syntax element dec_pic_size_idx (1102) in the tilegroup header (1101), and thus allowing different decoded sizes and zoomfactors per tile group.

According to an aspect of the disclosure, certain video codingtechnologies or standards (e.g., VP9) can enable spatial scalability byimplementing certain forms of reference picture resampling inconjunction with temporal scalability. In an embodiment, a referencepicture is upsampled using ARC-style technologies to a higher resolutionto form the base of a spatial enhancement layer. The upsampled picturecan be refined, using normal prediction mechanisms (e.g.,motion-compensated prediction for inter-prediction from referencepictures) at the high resolution for example to add detail.

In some examples, a value in a network abstraction layer (NAL) unitheader, for example, a temporal ID field, is used to indicate temporallayer information and also spatial layer information. Using the value inNAL unit header to indicate both temporal layer information and thespatial layer information can enable the usage of existing selectedforwarding units (SFUs) for scalable environment without modification.For example, the existing SFUs can be created and optimized for thetemporal layer selected forwarding, based on the NAL unit headertemporal ID value. Then, the existing SFUs can be used for spatialscalability (e.g., selection of spatial layers) without modification insome examples. In some examples, a mapping can be provided between acoded picture size and the temporal layer that is indicated by thetemporal ID field in the NAL unit header.

According to an aspect of the disclosure, some features of a codedbitstream can be specified using profile, tier and level combination(PTL) information that includes profile, tier, level and generalconstraint information. In some examples, a profile defines a subset offeatures of a bitstream, such as color reproduction, resolution,additional video compression and the like. A video codec can definevarious profiles, such as a baseline profile (e.g., a simple profilewith a low compression ratio), a high profile (a complex profile with ahigh compression ratio), a Main profile (e.g., a profile with a mediumcompression ratio between the baseline profile and the high profile, canbe the default profile setting), and the like.

Further, tiers and levels can be used to specify certain constrains thatdefine a bitstream in terms of maximum bit rate, maximum luma samplerate, maximum luma picture size, minimum compression ratio, maximumnumber of slices allowed, maximum number of tiles allowed, and the like.Lower tiers are more constrained than higher tiers and lower levels aremore constrained than higher levels. In an example, a standard maydefine two tiers: Main and High. The Main tier is a lower tier than theHigh tier. The tiers are made to deal with applications that differ interms of their maximum bit rate. The Main tier is designed for mostapplications while the High tier is designed for very demandingapplications in an example. A standard can define multiple levels. Alevel is a set of constraints for a bitstream. In an example, for levelsbelow level 4 only the Main tier is allowed. In some examples, a decoderthat conforms to a given tier/level is required to be capable ofdecoding all bitstreams that are encoded for that tier/level and for alllower tiers/levels.

General constraint information may include constraint information on thevideo source type, coding tool and functionalities. For example,constraint flags can indicate whether inter coding tools, intra codingtools, a DBF, entropy coding, a transform, partitioning (e.g., a tile, aslice), buffer management, random access (e.g., IDR), a parameter set(e.g., an SPS, a PPS), and/or the like are present or used in the codedvideo bitstream. The constraint information can be signaled in parametersets (e.g., an SPS, a VPS, or DCI). The constraint flags can be signaledin a high-level syntax structure (e.g., an SPS, a VPS, DCI).

According to some aspects of the disclosure, the PTL information can beassociated with a scope (e.g., a portion of coded video data in abitstream). In some examples, the PTL information can be specified for,for example, the entire bitstream, a CVS of the bitstream, each outputlayer set (OLS) of the bitstream, and/or the like, and can be signaledin a high-level syntax (HLS) structure, such as a VPS, a DPS, DCI, aSPS, a PPS, an APS, a GOP, a sequence, a header, an SEI message, or thelike.

In some examples, the high-level syntax (HLS) is defined with regard toblock level. Block-level coding tools can be used to decode pixels orsamples within a picture to reconstruct the picture. The block-levelcoding tools can include any suitable coding tools used inreconstruction of a coding block, such as coding tools for interprediction (or inter coding tools), coding tool(s) for intra prediction(or intra coding tools), an adaptive loop filter (ALF), a deblockingfilter (DBF), entropy coding, a transform, and the like.

High-level syntax (HLS) can specify information on functionality,system-interface, picture-level control of tools and buffer control, andthe like. For example, the HLS can specify partition (e.g., a tile, aslice, a subpicture), buffer management, random access (e.g., IDR, cleanrandom access (CRA)), parameter set(s) (e.g., a VPS, an SPS, a PPS, anAPS), reference picture resampling (RPR), scalability, and/or the like.The high-level syntax can be above a block-level.

Control information can have a suitable level, such as SPS level toolcontrol information, PPS level tool control information, sequence levelcontrol information, bitstream level control information, and/or thelike. In some examples, the PTL information is part of the controlinformation and can be signaled as constraint flags in an HLS structure,and can indicate control or constraint of tools in the scopecorresponding to the HLS structure. For example, the constraint flagsfor the PTL information can be provided in one of: sequence levelcontrol information and bitstream level control information. In anexample, if certain tools are disabled by constraint flags in an HLSstructure, and the tools are not used, for example, for coding blocks ina scope corresponding to the HLS.

FIG. 12 and FIG. 13 show an example of PTL information according to someembodiments of the disclosure. FIG. 12 shows a syntax structure example(1200) of a set of PTL syntax elements and FIG. 13 shows a syntaxstructure example (1300) of general constraint information.

In FIG. 12 , the set of PTL syntax elements can includegeneral_profile_idc, general_tier_flag, general_level_idc,num_sub_profiles, general_sub_profile_idc, sublayer_level_present_flag,ptl_alignment_zero_bit and sublayer_level_idc.

In FIG. 13 , the general constraint information can include a pluralityof constraint flags. In an example, a constraint flag (e.g., anintra_only_constraint_flag) (1305) equal to 1 can indicate that aparameter sh_slice_type should be I (i.e., a slice being an intraslice). The parameter sh_slice_type is a parameter in a slice headerthat specifies a coding type of the slice between types I, P and B. Theconstraint flag (e.g., the intra_only_constraint_flag) (1305) equal to 0does not impose the constraint (e.g., the sh_slice_type should be I) forall coded pictures within the scope of the PTL information where otherinformation (e.g., a profile_idc) can allow non intra-slices. In anotherexample, a constraint flag (e.g., a no_alf_constraint_flag) (1306) equalto 1 can indicate that an sps_alf_enabled_flag is equal to 0 for allCVSs within the scope of the PTL information, and thus adaptive loopfiltering is not in use even if the adaptive loop filtering is allowedbased, for example, on the profile_idc. The constraint flag (e.g., theno_alf_constraint_flag) (1306) equal to 0 does not impose the aboveconstraint.

In another example, a constraint flag (e.g., ano_lossless_coding_tool_constraint_flag) (1301) can be signaled in thegeneral constraint information, as shown in FIG. 13 . The constraintflag (e.g., the no_lossless_coding_tool_constraint_flag) (1301) equal to1 can indicate that coding tool(s) related to lossless coding cannot beused within the scope of the PTL information including the constraintflag (1301). The constraint flag (e.g., theno_lossless_coding_tool_constraint_flag) (1301) equal to 0 does notimpose the above constraint.

In another example, a constraint flag (e.g., ano_lossy_coding_tool_constraint_flag) (1302) can be signaled in thegeneral constraint information, as shown in FIG. 13 . The constraintflag (e.g., the no_lossy_coding_tool_constraint_flag) (1302) equal to 1can indicate that coding tool(s) related to lossy coding cannot be usedwithin the scope of the PTL information including the constraint flag(1302). The constraint flag (e.g., theno_lossy_coding_tool_constraint_flag) (1302) equal to 0 does not imposethe above constraint.

In an embodiment, the constraint flag (e.g., theno_lossless_coding_tool_constraint_flag) (1301) may not be equal to 1when the constraint flag (e.g., theno_lossy_coding_tool_constraint_flag) (1302) is equal to 1.Alternatively, the constraint flag (e.g., theno_lossy_coding_tool_constraint_flag) (1302) may not be equal to 1 whenthe constraint flag (e.g., the no_lossless_coding_tool_constraint_flag)(1301) is equal to 1.

The plurality of constraint flags in the general constraint informationcan be sorted in certain orders. The order can be set based on, forexample, likelihoods of respective mechanisms and/or tools not beingused in a scope of a PTL. The order can be referred to as a priorityorder. The order can be presented in the general constraint informationsyntax structure from a high priority to a low priority where the highpriority indicates that non-use of a tool (or a mechanism) has a highlikelihood and the low priority indicates that non-use of the tool (orthe mechanism) has a low likelihood. Additional factors affecting theorder can include tools likely being used only for specific use cases(e.g., tools for sub-pictures, scalability, and/or interlace support),impact of the tool for encoder/decoder/implementation complexity, andthe like.

FIGS. 14A-14B show examples of PTL information that includes a syntaxstructure example (1410) of PTL syntax structure (also referred to asPTL bracket) and a syntax example (1420) for general constraintinformation syntax structure (also referred to as general constraintinformation bracket) according to some embodiments of the disclosure. Insome example, a syntax element indicating a number of constraint flags(e.g., a num_available_constraint_flags) can be signaled. In an example,the syntax element indicating the number of constraints flag can besignaled in the PTL syntax structure, such as shown by (1401) in thesyntax example (1410) as shown in FIG. 14A that can be outside of thesyntax example (1420) for the general constraint information bracket.Alternatively, the syntax element indicating the number of constraintflags can be signaled in a beginning of the general constraintinformation bracket, such as the beginning of the syntax example (1420).When the syntax element (e.g., the num_available_constraint_flags) ispresent and a value of the syntax element (e.g., thenum_available_constraint_flags) is equal to N, the first N constraintflags may be present in the general constraint information syntaxstructure. Further, other constraint flags may not be present and can beinferred to be equal to a specific value. N can be a non-negativeinteger.

In an embodiment, the value N (e.g., the num_available_constraint_flags)is in a range of 0 to a maximum number of constraint flags (e.g., avalue of a parameter MaxNumConstraintFlags). The maximum number ofconstraint flags can be any positive integer. The value of the maximumnumber of constraint flags (e.g., MaxNumConstraintFlags) can bepredefined to be 16, 32, 64, 128, or the like. When the value N (e.g.,num_available_constraint_flags) is equal to 0, no constraint flags arepresent in the general constraint information syntax structure. Codingof the value N (e.g., num_available_constraint_flags) can be chosen suchthat a corresponding entropy-coded representation for the value N andthe constraint flags can add up to a number divisible by 8 to ensurebyte alignment.

In some examples, constraint flags can be categorized into one or moreconstraint information groups. Each constraint information group caninclude one or more constraint flags and can have a corresponding gateflag. A gate flag of a corresponding constraint information group canindicate whether constraint flag(s) in the corresponding constraintinformation group may be present. In an example, the gate flag can bereferred to as a constraint group present flag. In general, the gateflag is associated with the corresponding constraint information group,and is associated with constraint flag(s) in the correspondingconstraint information group. In an embodiment, the gate flag gateswhether the constraint flag(s) in the corresponding constraintinformation group are present (or signaled) in constraint information.For example, if the gate flag of the corresponding constraintinformation group is equal to 1, the constraint flag(s) corresponding tothe constraint information group can be present, for example, in thegeneral constraint information. If the gate flag of the correspondingconstraint information group is equal to 0, the constraint flag(s)corresponding to the constraint information group may not be present,for example, in the general constraint information. In an example, ifall the gate flags are equal to 0, no constraint flags are present.

Constraint flags can have different copes. For example, a scope ofconstraint flags in DCI can be a coded video bitstream. A scope ofconstraint flags in a VPS can be CLVSs with multiple layers. A scope ofconstraint flags in an SPS can be a single CLVS.

FIGS. 15A-15B show an example of a general constraint information syntaxstructure (1500) according to an embodiment of the disclosure. Thegeneral constraint information syntax structure (1500) includes flagsthat represent general constraint information. Specifically, the generalconstraint information syntax structure (1500) includes one or more gateflags, such as a gate flag (e.g., ageneral_frame_structure_constraint_group_flag) (1501), a gate flag(e.g., a high_level_functionality_constraint_group_flag) (1502), a gateflag (e.g., a scalability_constraint_group_flag) (1503), a gate flag(e.g., a partitioning_constraint_group_flag) (1504), a gate flag (e.g.,an intra_coding_tool_constraint_group_flag) (1505), a gate flag (e.g.,an inter_coding_tool_constraint_group_flag) (1506), a gate flag (e.g., atransfom_contraint_group_flag) (1507), a gate flag (e.g., aninloop_filtering_constraint_group_flag) (1508) in FIG. 15A. The one ormore gate flags (e.g., the gate flags (1501)-(1508)) can be present atthe beginning of the general constraint information syntax structure(1500), as shown in FIG. 15A.

The gate flag (e.g., the general_frame_structure_constraint_group_flag)(1501) is associated with a constraint information group (1510), and isassociated with constraint flags (1511)-(1514) that are in theconstraint information group (1510). The gate flag (e.g., thegeneral_frame_structure_constraint_group_flag) (1501) being equal to 1can specify that the constraint flags (1511)-(1514) that are in theconstraint information group (1510) may be present.

The constraint information group (1510) (or the constraint flags(1511)-(1514)) can be related to input source and frame packing (e.g. apacked or a projected frame). Referring to FIG. 15A, the constraintflags (1511)-(1514) correspond to a general_non_packed_constraint_flag(1511), a general_frame_only_constraint_flag (1512), ageneral_non_projected_constraint_flag (1513), and a genera_one_picture_only_constraint_flag (1514). Otherwise, the gate flag (e.g.,the general_frame_structure_constraint_group_flag) (1501) being equal to0 can specify that constraint flags (1511)-(1514) that are in aconstraint information group (1510) may not be present in the generalconstraint information syntax structure (1500).

Further, in some examples, the gate flag (e.g., thehigh_level_functionality_constraint_group_flag) (1502) being equal to 1can specify that constraint flags related to high level functionality(e.g. reference picture resampling) that are in a constraint informationgroup (1520) may be present as shown by FIG. 15B. Otherwise, the gateflag (e.g., the high_level_functionality_constraint_group_flag) (1502)being equal to 0 can specify that the constraint flags that are in theconstraint information group (1520) may not be present in the generalconstraint information syntax structure (1500).

Referring back to FIG. 15A, the gate flag (e.g., thescalability_constraint_group_flag) (1503) being equal to 1 can specifythat constraint flag(s) related to scalability (e.g. interlayerprediction) may be present. Otherwise, the constraint flag(s) related tothe scalability may not be present in the general constraint informationsyntax structure (1500).

The gate flag (e.g., the partitioning_constraint_group_flag) (1504)being equal to 1 can specify that constraint flag(s) related to highlevel partitioning (e.g. a subpicture or a tile) may be present.Otherwise, the constraint flags related to the high level partitioningmay not be present in the general constraint information syntaxstructure (1500).

The gate flag (e.g., the intra_coding_tool_constraint_group_flag) (1505)being equal to 1 can specify that constraint flag(s) related to intracoding (e.g. intra prediction) may be present. Otherwise, the constraintflag(s) related to the intra coding may not be present in the generalconstraint information syntax structure (1500).

The gate flag (e.g., the inter_coding_tool_constraint_group_flag) (1506)being equal to 1 can specify that constraint flag(s) related to intercoding (e.g. motion compensation for inter-picture prediction) may bepresent. Otherwise, the constraint flags related to the inter coding maynot be present in the general constraint information syntax structure(1500).

The gate flag (e.g., the transfom_contraint_group_flag) (1507) beingequal to 1 can specify that constraint flag(s) related to transformcoding (e.g. multiple transform matrices) may be present. Otherwise, theconstraint flags related to the transform coding may not be present inthe general constraint information syntax structure (1500).

In an embodiment, when all gate flags (e.g., the gate flags(1501)-(1508) in FIG. 15A) are equal to 0, no constraint flags arepresent in the general constraint information syntax structure (e.g.,the general constraint information syntax structure (1500)).

According to aspects of the disclosure, syntax can be designed such thatcontrol information including gate flags (e.g., the gate flags(1501)-(1508)), associated constraint flags (e.g., the constraint flags(1511)-(1512) and the constraint flags in the constraint informationgroup (1520)), additional control information, and/or the like can bebyte aligned, for example, a number of flags is divisible by 8 topreserve the byte alignment. In an example, a number of gate flags andconstraint flags in constraint information (e.g., the general constraintinformation syntax structure (1500)) is divisible by 8. A byte-alignmentmechanism can be used to achieve the byte-alignment of the controlinformation. Referring to FIG. 15B, syntax (e.g., a while loop) (1530)can be used for byte-alignment.

In some embodiments, offset information, such as an offset (e.g., usinga syntax element constraint_info_offset[ ])) and length information,such as a length (e.g., using a syntax element constraint_info_length[]) are present in the constraint information (e.g., at the beginning ofa general constraint information syntax structure) to assist presentingconstraint flag(s) in the respective constraint information group(s)associated with the gate flag(s) in the constraint information. In anembodiment, one or more of the at least one constraint information groupare present in the coded video bitstream. For a constraint informationgroup, an offset and a length can be present in the constraintinformation for the constraint information group. The offset canindicate the offset to a first constraint flag in the constraintinformation group, and the length can indicate the number of constraintflags in the constraint information group. In some examples, the numberof constraint information groups can be explicitly indicated, forexample, by a syntax element num_constraint_info_set. The value ofnum_constaint_info_set can be an integer that is larger than or equal to0. When the value of num_constaint_info_set is 0,constraint_info_offset[ ], constraint_info_length[ ] and constraintflags are not present in the general constraint information syntaxstructure.

In an embodiment, a constraint information offset (e.g., a syntaxelement constraint_info_offset[i]) and a constraint information length(e.g., a syntax element constraint_info_length[i]) can assist presentingconstraint flags for the constraint information group i (i is a positiveinteger) in the constraint information (e.g., the general constraintinformation syntax structure). In an example, when a value of theconstraint information offset (e.g., the syntax elementconstraint_info_offset[i]) is equal to 5, and a value of the constraintinformation length (e.g., the syntax element constraint_info_length[i])is equal to 3, the fifth, the sixth, and the seventh constraint flagsare associated with the constraint information group i and are presentin the constraint information (e.g., the general constraint informationsyntax structure).

In an example, a run-length coding can be used to code the constraintflags that are specified in a pre-determined order (or a given order).

In an embodiment, a run-coding can be used where the constraint flagsare specified in a pre-determined order (or a given order). Instead ofcoding the constraint flags directly, a suitably coded list of “skip”values can indicate constraint flags that are equal to zero, with afollowing constraint flag being implied to be equal to 1. The run-codingdescribed above may be particularly efficient if (i) a number of theconstraint flags is large and (ii) a small percentage of the constraintflags is equal to 1.

In an embodiment, one or more of the at least one constraint informationgroup are present in the coded video bitstream. A plurality ofconstraint flags in the one or more of the at least one constraintinformation group is signaled according to the predetermined order.Accordingly, the plurality of constraint flags can be run-coded (e.g.,run-encoded or run-decoded). Further, the prediction information for thesubset of coding blocks can be determined based on the plurality ofconstraint flags.

In an embodiment, the at least one constraint flag in the constraintinformation group of the gate flag includes a plurality of constraintflags signaled according to a predetermined order. Accordingly, theplurality of constraint flags can be run-coded (e.g., run-encoded orrun-decoded).

In an embodiment, a full list of the constraint flags can be specifiedin a video coding standard (e.g., a VVC specification), an externaltable, or the like. In an example, only available constraint flag(s) ofthe constraint flags are indicated, for example, by one or more of thefollowing: a number of available constraint flags (e.g., anum_available_constraint_flags), gate flag(s) (or constraint grouppresent flag(s)), constraint information offset information andconstraint information length information, or the like are present inthe coded video stream.

In an example, a full list of the constraint flags is specified and isavailable to an encoder and a decoder. The full list of the constraintflags can be stored at the decoder. The full list of the constraintflags can include 100 constraint flags. 10 of the 100 constraint flagsare present in constraint information for a CLVS and thus are availableto the subset of coding blocks in the CLVS. The 10 of the 100 constraintflags are referred to as the 10 available constraint flags. In anexample, a number of available constraint flags (e.g., 10) is signaled.In an example, the 10 available constraint flags are in two constraintinformation groups and are gated by a first gate flag and a second gateflag. Thus, the first gate flag and the second gate flag can be signaledto indicate the 10 available constraint flags.

In an example, a first constraint information offset (e.g., the syntaxelement constraint_info_offset[0]) and a first constraint informationlength (e.g., the syntax element constraint_info_length[0]) aresignaled. A second constraint information offset (e.g., the syntaxelement constraint_info_offset[1]) and a second constraint informationlength (e.g., the syntax element constraint_info_length[1]) aresignaled. For example, the syntax element constraint_info_offset[0] is15 and the syntax element constraint_info_length[0] is 3, and the syntaxelement constraint_info_offset[1] is 82 and the syntax elementconstraint_info_length[1] is 7,and thus indicate that the 15th to the17th constraint flags and the 82th to the 88th constraint flags in thefull list (e.g., the 100 constraint flags) are available or present inthe constraint information.

In an embodiment, any of the various techniques (or methods,embodiments, examples) for efficient coding of constraint flags can becombined, employing suitable control information. The combination may bea suitable combination of two or more of such techniques. Alternatively,one of the various techniques (or methods, embodiments, examples) can beused independently. Constraint flags can be grouped. In certaingroup(s), run-coding can be used while other group(s) may employstraightforward binary coding.

The value of the maximum number of constraint flags (e.g.,MaxNumConstraintFlags) can be predefined to be 16, 32, 64, 128, or thelike.

The value of the maximum number of constraint flags (e.g.,MaxNumConstraintFlags) can be determined by the profile information,such as general_profile_idc or general_sub_profile_idc, or a codecversion information, so that the range of the number of constraint flags(e.g., the num_available_constraint_flags (1401)) can be restricted bythe profile information or the version information. For example, thevalue of the number of constraint flags (e.g., thenum_available_constraint_flags (1401)) in a main profile (e.g., wherethe MaxNumConstraintFlags=64) can be in the range of 0 to 64, while thevalue of the number of constraint flags (e.g., thenum_available_constraint_flags (1401)) in an advanced profile (e.g.,where MaxNumConstraintFlags=128) can be in the range of 0 to 128.

In an embodiment, the value of the number of constraint flags (e.g., thenum_available_constraint_flags) can be inferred to be equal to a valuepredefined by the profile information, such as general_profile_idc orgeneral_sub_profile_idc, or codec version information, so that the valueof num_available_constraint_flags can be determined without explicitlysignaling.

In some embodiments, reserved byte information can be present in thegeneral constraint information syntax structure. For example, as shownin FIG. 13 , the flags gci_num_reserved_bytes (1303) andgci_reserved_bytes[ ] (1304) can be present in the general constraintinformation syntax structure for extension of the general constraintinformation syntax structure. The flag gci_num_reserved_ bytes canspecify a number of reserved constraint bytes. In an example, thereserved constraint bytes are for signaling additional flags (e.g.,additional constraint flags). The flag gci_reserved_byte[ ] may have anysuitable value.

In an embodiment, a value of gci_num_reserved_bytes may be restricted ordetermined by the profile information, such as general_profile_idc orgeneral_sub_profile_idc, or codec version information. With a baseprofile (or the main profile), the value of the flaggci_num_reserved_bytes can be 0. With an extended profile (or theadvanced profile), the value of gci_num_reserved_bytes can be greaterthan 0.

In some embodiments, a field sequence flag can be signaled in a codedvideo bitstream. The field sequence flag can indicate whether picturesin an output layer are coded with field coding. In some examples, thefield sequence flag can be signaled in an SPS using a syntax element ansps_field_seq_flag. In an embodiment, the flag sps_field_seq_flag may bepresent in an SPS. The flag sps_field_seq_flag being equal to 1 canindicate that a CLVS conveys pictures that represent fields. The flagsps_field_seq_flag being equal to 0 can indicate that the CLVS conveyspictures that represent frames.

In the general constraint information syntax structure in FIG. 13 , theflag general_frame_only_constraint_flag may be present. The flaggeneral_frame_only_constraint_flag being equal to 1 can specify that ascope for an output layer set (e.g., OlsInScope) conveys pictures thatrepresent frames. The flag general_frame_only_constraint_flag beingequal to 0 specifies that the scope for the output layer set (e.g., theOlsInScope) conveys pictures that may or may not represent frames. In anembodiment, the flag general_frame_only_constraint_flag indicateswhether pictures in an output layer set is coded with field coding. Theoutput layer set can include the subset of coding blocks. The flagsps_field_seq_flag can be false based on the flaggeneral_frame_only_constraint_flag (e.g., being 1) indicating that asubset of the pictures is not coded with field coding. The subset of thepictures can be in one layer of the output layer set.

When the flag general_frame_only_constraint_flag is equal to 1, thevalue of the flag sps_field_seq_flag may be equal to 0.

In an embodiment, the flag pps_mixed_nalu_types_in_pic_flag may bepresent in a PPS. The flag pps_mixed_nalu_types_in_pic_flag being equalto 1 can specify that each picture referring to the PPS has more thanone VCL NAL unit and the VCL NAL units do not have the same value ofnal_unit_type. The flag pps_mixed_nalu_types_in_pic_flag being equal to0 can specify that each picture referring to the PPS has one or more VCLNAL units and the VCL NAL units of each picture referring to the PPShave the same value of nal_unit_type. In the general constraintinformation syntax structure in FIG. 13 , the flagno_mixed_nalu_types_in_pic_constraint_flag may be present. The flagno_mixed_nalu_types_in_pic_constraint_flag being equal to 1 can specifythat the value of pps_mixed_nalu_types_in_pic_flag shall be equal to 0.The flag no_mixed_nalu_types_in_pic_constraint_flag being equal to 0does not impose such a constraint.

In an embodiment, the flag general_one_picture_only_constraint_flag maybe present in the general constraint information syntax structure, suchas shown in FIG. 13 . The general_one_picture_only_constraint_flag beingequal to 1 can specify that there is only one coded picture in abitstream. The flag general_one_picture_only_constraint_flag being equalto 0 does not impose such a constraint.

In an embodiment, the flag single_layer_constraint_flag may be presentin the general constraint information syntax structure, such as shown inFIG. 13 . The flag single_layer_constraint_flag being equal to 1 canspecify that a sps_video_parameter_set_id shall be equal to 0. The flagsingle_layer_constraint_flag being equal to 0 does not impose such aconstraint. When the flag general_one_picture_only_constraint_flag isequal to 1, the value of the flag single_layer_constraint_flag may beequal to 1.

In an embodiment, the flag all_layers_independent_constraint_flag may bepresent in the general constraint information syntax structure, such asshown in FIG. 13 . The flag all_layers_independent_constraint_flag beingequal to 1 can specify that a flag vps_all_independent_layers_flag maybe equal to 1. The flag all_layers_independent_constraint_flag beingequal to 0 does not impose such a constraint. When the flagsingle_layer_constraint_flag is equal to 1, the value of the flagall_layers_independent_constraint_flag may be equal to 1.

In an embodiment, the flag no_res_change_in_clvs_constraint_flag may bepresent in the general constraint information syntax structure, such asshown in FIG. 13 . The flag no_res_change_in_clvs_constraint_flag beingequal to 1 can specify that a flag sps_res_change_in_clvs_allowed_flagmay be equal to 0. The flag no_res_change_in_clvs_constraint_flag beingequal to 0 does not impose such a constraint. When the flagno_ref_pic_resampling_constraint_flag to 1, the value of the flagno_res_change_in_clvs_constraint_flag may be equal to 1.

In an embodiment, the flag no_mixed_nalu_types_in_pic_constraint_flagmay be present in the general constraint information syntax structure inFIG. 13 . The flag no_mixed_nalu_types_in_pic_constraint_flag beingequal to 1 specifies that the value of the flagpps_mixed_nalu_types_in_pic_flag may be equal to 0. The flagno_mixed_nalu_types_in_pic_constraint_flag being equal to 0 does notimpose such a constraint. When a flag one_subpic_per_pic_constraint_flagis equal to 1, the value of the flagno_mixed_nalu_types_in_pic_constraint_flag may be equal to 1.

In an embodiment, the flag no_trail_constraint_flag may be present inthe general constraint information syntax structure in FIG. 13 . Theflag no_trail_constraint_flag being equal to 1 can specify that theremay be no NAL unit with a nuh_unit_type equal to TRAIL_NUT present inOlsInScope (the OlsInScope is output layer set that includes all layersin the entire bitstream that refers to the DPS). The flagno_trail_constraint_flag being equal to 0 does not impose such aconstraint. When the flag general_one_picture_only_constraint_flag isequal to 1, the flag no_trail_constraint_flag may be equal to 1.

In an embodiment, the flag no_stsa_constraint_flag may be present ingeneral constraint information syntax structure in FIG. 13 . The flagno_stsa_constraint_flag being equal to 1 can specify that there may beno NAL unit with the nuh_unit_type equal to STSA_NUT present inOlsInScope. The flag no_stsa_constraint_flag being equal to 0 does notimpose such a constraint. When the flaggeneral_one_picture_only_constraint_flag is equal to 1, the flagno_stsa_constraint_flag may be equal to 1.

In an embodiment, the flag no_trail_constraint_flag may be present inthe general constraint information syntax structure in FIG. 13 . Theflag no_trail_constraint_flag being equal to 1 can specify that theremay be no NAL unit with the nuh_unit_type equal to TRAIL_NUT present inOlsInScope. The flag no_trail_constraint_flag being equal to 0 does notimpose such a constraint. When the flaggeneral_one_picture_only_constraint_flag is equal to 1, the flagno_trail_constraint_flag may be equal to 1.

In an embodiment, the flag no_stsa_constraint_flag may be present in thegeneral constraint information syntax structure in FIG. 13 . The flagno_stsa_constraint_flag being equal to 1 can specify that there may beno NAL unit with the nuh_unit_type equal to STSA_NUT present inOlsInScope. The flag no_stsa_constraint_flag being equal to 0 does notimpose such a constraint. When the flaggeneral_one_picture_only_constraint_flag is equal to 1, the flagno_stsa_constraint_flag may be equal to 1.

In an embodiment, the flag no_idr_constraint_flag may be present in thegeneral constraint information syntax structure, such as shown in FIG.13. The no_idr_constraint_flag being equal to 1 can specify that theremay be no NAL unit with the nuh_unit_type equal to IDR_W_RADL orIDR_N_LP present in OlsInScope. The flag no_idr_constraint_flag beingequal to 0 does not impose such a constraint.

In an embodiment, the flag no_cra_constraint_flag may be present in thegeneral constraint information syntax structure, such as shown in FIG.13 . The flag no_cra_constraint_flag being equal to 1 can specify thatthere may be no NAL unit with the nuh_unit_type equal to CRA_NUT presentin OlsInScope. The flag no_cra_constraint_flag being equal to 0 does notimpose such a constraint.

In an embodiment, the flag no_rasl_constraint_flag may be present in thegeneral constraint information syntax structure in FIG. 13 (the flagno_rasl_constraint_flag is not shown). The flag no_rasl_constraint_flagbeing equal to 1 can specify that there may be no NAL unit with thenuh_unit_type equal to RASL_NUT present in OlsInScope. The flagno_rasl_constraint_flag being equal to 0 does not impose such aconstraint. When the flag no_cra_constraint_flag is equal to 1, thevalue of the flag no_rasl_constraint_flag may be equal to 1.

In an embodiment, the flag no_radl_constraint_flag may be present in thegeneral constraint information syntax structure, such as shown in FIG.13 . The flag no_radl_constraint_flag being equal to 1 can specify thatthere may be no NAL unit with the nuh_unit_type equal to RADL_NUTpresent in OlsInScope. The flag no_radl_constraint_flag being equal to 0does not impose such a constraint. When the flag no_idr_constraint_flagis equal to 1 and the flag no_cra_constraintflag is equal to 1, thevalue of the flag no_rasl_constraint_flag may be equal to 1.

Some aspects of the disclosure provide techniques for constraint flagsignaling for range extensions, such as range extension with positioncoding for the last significant coefficient in residual coding.

According to an aspect of the disclosure, some standards can bedeveloped originally for certain applications with specific chromaformat and specific bitdepths (bits per sample). For example, HEVCoriginally targets applications with 4:2:0 chroma format at 8-10 bitsper sample. To make a standard applicable to other formats and bitdepthsbesides the specific chroma format and the specific bitdepths, rangeextensions are developed to support applications that use other chromaformats and/or higher bitdepths.

In order to restrict the feature set to what is needed for a particulargroup of applications, video coding standards define profiles, which caninclude defined decoder feature sets to be supported forinteroperability with encoders that use these features. For example, aprofile can define a set of coding tools or algorithms that can be usedin generating a conforming bitstream. In addition to profiles, somestandards (e.g., VVC, HEVC and the like) also defines levels and tiers.A level imposes restrictions on the bitstream related to spatialresolution, pixel rate, bit rate values and variations that maycorrespond to decoder processing load and memory capabilities. Levelrestrictions can be represented in terms of maximum samples rate,maximum picture size, maximum bit rate, minimum compression ratio,capacities of coded picture buffer, and the like. Higher values of levelcan correspond to higher complexity limits. Tiers modify the bit ratevalue and variation limits for each level. For example, the Main tier isintended for most applications, while the High tier is designed toaddress video contribution applications that are more demanding, such ashave significantly higher bit rate values than video distributionapplications. Each of profile, tier, and level affects theimplementation and decoding complexities, and a combination of the threespecifies an interoperability point for bitstreams and decoders.

In some examples, a decoder conforming to a certain tier and level isrequired to be capable of decoding all bitstreams that conform to thesame tier or the lower tier of that level or any level below it, anddecoders conforming to a specific profile can support all features inthat profile. In some examples, encoders are not required to make use ofany particular set of features supported in a profile, but are requiredto produce conforming bitstreams, i.e., bitstreams that obey thespecified constraints that enable them to be decoded by conformingdecoders.

In addition to the PTL information, a PTL syntax structure may alsoinclude a general constraints information (GCI) syntax structure, whichincludes a list of constraint flags and non-flag syntax elementsindicating specific constraint properties of the bitstream.

In an example, HEVC originally includes three profiles that are referredto as Main profile, Main 10 profile and Main Still Picture profile. Thethree profiles have some restrictions, such as supporting only 4:2:0chroma sampling. In the Main and Main Still Picture profiles, only avideo precision of 8 bits per sample is supported, while the Main 10profile supports up to 10 bits per sample. In the Main Still Pictureprofile, the entire bitstream includes only one coded picture.

In some examples, the HEVC with range extensions can support additionalprofiles. In an example, the following profiles are collectivelyreferred to as range extension profiles: Monochrome profile, Monochrome10 profile, Monochrome 12 profile, Monochrome 16 profile, Main 12profile, Main 4:2:2 10 profile, Main 4:2:2 12 profile, Main 4:4:4profile, Main 4:4:4 10 profile, Main 4:4:4 12 profile, Main Intraprofile, Main 10 Intra profile, Main 12 Intra profile, Main 4:2:2 10Intra profile, Main 4:2:2 12 Intra profile, Main 4:4:4 Intra profile,Main 4:4:4 10 Intra profile, Main 4:4:4 12 Intra profile, Main 4:4:4 16Intra profile, Main 4:4:4 Still Picture profile and Main 4:4:4 16 StillPicture profile.

Some of the range extension profiles can support higher bitdepth and canbe referred to as profiles for operation range extensions with highbitdepth. In some examples, the profiles for operation range extensionswith high bitdepth include profiles that support more than 10 bits persample, such as Main 12 profile, Main 12 4:4:4 profile, Main 16 4:4:4profile, Main 12 Intra profile, Main 12 4:4:4 Intra profile, Main 164:4:4 Intra profile, Main 12 Still Picture profile, Main 12 4:4:4 StillPicture profile, Main 16 4:4:4 Still Picture profile and the like.

Specifically, the Main 12 profile allows for a bit depth of 8 bits to 12bits per sample with support for 4:0:0 and 4:2:0 chroma sampling, bothintra prediction and inter prediction modes. In some examples, decodersthat conform to the Main 12 profile are capable of decoding bitstreamsmade with the following profiles: Monochrome, Monochrome 12, Main, Main10, and Main 12.

The Main 12 4:4:4 profile allows for a bit depth of 8 bits to 12 bitsper sample with support for 4:0:0, 4:2:0, 4:2:2, and 4:4:4 chromasampling, and both intra prediction and inter prediction modes. In someexamples, decoders that conform to the Main 12 4:4:4 profile are capableof decoding bitstreams made with the following profiles: Monochrome,Main, Main 10, Main 12, Main 10 4:2:2, Main 12 4:2:2, Main 4:4:4, Main10 4:4:4, Main 12 4:4:4, and Monochrome 12.

The Main 16 4:4:4 profile allows for a bit depth of 8 bits to 16 bitsper sample with support for 4:0:0, 4:2:0, 4:2:2, and 4:4:4 chromasampling, and both intra prediction and inter prediction modes.

The Main 12 Intra profile allows for a bit depth of 8 bits to 12 bitsper sample with support for 4:0:0 and 4:2:0 chroma sampling, and intraprediction mode.

The Main 12 4:4:4 Intra profile allows for a bit depth of 8 bits to 12bits per sample with support for 4:0:0, 4:2:0, 4:2:2, and 4:4:4 chromasampling, and intra prediction mode.

The Main 16 4:4:4 Intra profile allows for a bit depth of 8 bits to 16bits per sample with support for 4:0:0, 4:2:0, 4:2:2, and 4:4:4 chromasampling, and intra prediction mode.

The Main 12 Still Picture profile allows for a bit depth of 8 bits to 12bits per sample with support for 4:0:0 and 4:2:0 chroma sampling. In theMain 12 Still Picture profile, the entire bitstream includes only onecoded picture.

The Main 12 4:4:4 Still Picture profile allows for a bit depth of 8 bitsto 12 bits per sample with support for 4:0:0, 4:2:0, 4:2:2, and 4:4:4chroma sampling. In the Main 12 4:4:4 Still Picture profile, the entirebitstream includes only one coded picture.

The Main 16 4:4:4 Still Picture profile allows for a bit depth of 8 bitsto 16 bits per sample with support for 4:0:0, 4:2:0, 4:2:2, and 4:4:4chroma sampling. In the Main 16 4:4:4 Still Picture profile, the entirebitstream includes only one coded picture.

According some aspects of the disclosure, coding tool controls can beperformed at various scopes (e.g., a portion of coded video data that iscoded with the persistence of an instance of a syntax element for acoding tool control), such as a scope of a bitstream, a scope of a codedlayer video sequence (CLVS), a picture, a slice of a picture and thelike. In some examples, a coding tool control can be provided in ageneral constraint information (GCI) syntax structure that generallyincludes constraint information for a bitstream. In some examples, acoding tool control can be provided in a sequence parameter set (SPS)associated with a CLVS, the SPS generally includes information for theCLVS. In some examples, a coding tool control can be provided in a sliceheader of a slice, the slice header generally includes information forthe slice.

According to an aspect of the disclosure, control information for thecoding tools in the range extension can be provided at the variousscopes. In some examples, using a syntax element of a larger scope mayimprove coding efficiency. For example, a GCI syntax element valuegreater than 0 indicates that the bitstream is constrained in aparticular way, typically to indicate that a particular coding tool isnot used in the bitstream. Further, the GCI syntax element value equalto the value 0 signals that the associated constraint may not apply,such that the associated coding tool is allowed (but not required) to beused in the bitstream (if its use is supported in the indicatedprofile).

According to another aspect of the disclosure, when a coding tool is notused in coding of video data in a bitstream, indicating the no use ofthe coding tool, for example, in the PTL information and/or generalconstraint information, a video decoder without support of the codingtool may determine that the video decoder is able to decode thebitstream based on the signaling in the PTL information and/or thegeneral constraint information, and the functionality of the videodecoder can be extended.

In some embodiments, an encoder can produce a bitstream conforming to avideo standard with range extension, but does not make use of one ormore features supported in the range extension. In some examples, withthe knowledge of no use of the one or more features in the rangeextension, a decoder conforming to the video standard but not supportingthe one or more features in the range extension may determine that thedecoder is able to decode the bitstream, and may accept the bitstreamfor decoding instead of rejecting the bitstream.

FIG. 16 shows a syntax structure (1600) of general constraintinformation according to some embodiments of the disclosure. In someexamples, the syntax structure (1600) includes constraints to be appliedto a bitstream, such as a bitstream including an output layer set to adecoder. In the FIG. 16 example, a syntax element denoted bygci_num_additional_bits in the syntax structure (1600) is used tospecify a number of additional general constraint information (GCI) bitsin the general constraint information syntax structure (1600) other thanalignment zero bits syntax elements (when present). In some standards,the value of gci_num_additional_bits is required to be equal to 0 or 1.In some standards, decoders may allow values of gci_num_additional_bitsgreater than 1 to appear in the syntax structure.

In the FIG. 16 examples, the syntax structure (1600) includes 5additional GCI bits (syntax elements) (1601)-(1605) denoted bygeneral_no_extended_precision_constraint_flag,general_no_ts_residual_coding_rice_present_in_sh_constraint_flag,general_no_rrc_rice_extension_constraint_flag,general_no_persistent_rice_adaptation_constraint_flag, andgeneral_no_reverse_last_sig_coeff_constraint_flag. The 5 additional GCIbits (1601)-(1605) respectively provide coding control information ofcoding tools in the scope of a bitstream of an output layer set in someexamples

FIG. 17 shows a syntax structure (1700) example of sequence parameterset (SPS) range extension according to some embodiments of thedisclosure. The syntax structure (1700) can be added in a SPS for a CLVSto provide control of coding tools of range extension for the CLVS. Thesyntax structure (1700) includes 5 syntax elements (1701)-(1705) thatare denoted by sps_extended_precision_flag,sps_ts_residual_coding_rice_present_in_sh_flag,sps_rrc_rice_extension_flag,sps_persistent_rice_adaptation_enabled_flag, andsps_reverse_last_sig_coeff_enabled_flag. The 5 syntax elements(1701)-(1705) provide coding control information of coding tools in thescope of a CLVS in some examples.

Specifically, in an embodiment, the GCI bit (1601) and the syntaxelement (1701) are used to provide, in different scopes, control ofusing an extended precision, such as control of a coding tool of theextended dynamic range for transform coefficients in the scaling andtransformation processes and for binarization of some syntax elements,such as abs_remainder[ ] and dec_abs_level[ ] and the like.

The syntax element (1701) equal to 1 specifies that an extended dynamicrange is used for transform coefficients in the scaling andtransformation processes and for binarization of some syntax elements,such as abs_remainder[ ] and dec_abs_level[ ] and the like. The syntaxelement abs_remainder[scanning position n] is the remaining absolutevalue of a transform coefficient level that is coded with Golomb-Ricecode at the scanning position n. When abs_remainder[ ] is not present,it is inferred to be equal to 0. The syntax elementdec_abs_level[scanning position n] can correspond to an intermediatevalue that is coded with Golomb-Rice code at the scanning position n andis used to determine the level of the transform coefficient at thescanning position n. The syntax element (1701) equal to 0 specifies thatthe extended dynamic range is not used in the scaling and transformationprocesses and is not used for binarization of, for example, the syntaxelements abs_remainder[ ] and dec_abs_level[ ] and the like. When notpresent, the value of the syntax element (1701) is inferred to be equalto 0.

In an example, a variable denoted by Log2TransformRange is used todetermine the dynamic range for transform coefficients in the scalingand transformation processes and for binarization of certain syntaxelements. For example, the variable Log2TransformRange can be the numberof bits for representing the transform coefficients in the scaling andtransformation processes and for binarization of certain syntaxelements. The dynamic range can be a difference of a largest number anda smallest number represented using the number of bits. In an example,the variable Log2TransformRange is derived according to the syntaxelement (1701) sps_extended_precision_flag, such as using Eq. (1):

Log2TransformRange=sps_extended_precision_flag?Max(15, Min(20,BitDepth+6)):15    Eq. (1)

The dynamic range for transform coefficients in the scaling andtransformation processes and for binarization of certain syntax elementscan be determined based on the variable Log2TransformRange. In someexamples, when the flag sps_extended_precision_flag has value 0, theextended dynamic range feature (e.g., a coding tool of the extendeddynamic range) is not used, and the dynamic range of the transformcoefficients is based on a fixed number of bits, such as 15 bits. Whenthe flag sps_extended_precision_flag has value 1, the extended dynamicrange feature is enabled, and the number of bits to represent thetransform coefficients in the scaling and transform processing can beone of 15 bits, 16 bits, 17 bits, 18 bits, 19 bits, and 20 bits based onthe bitdepth BitDepth in the Eq. (1) example. The dynamic range of thetransform coefficients can be determined based on the number of bits.

According to an aspect of the disclosure, a syntax element (e.g.,denoted by sps_bitdepth_minus8) can be used to signal the bit depth ofthe samples of the luma and chroma arrays (e.g., denoted BitDepth), andthe value of the luma and chroma quantization parameter range offset(e.g., denoted by QpBdOffset). In an example, the bit depth BitDepth canbe calculated according to Eq. (2), and the QP range offset QpBdOffsetcan be calculated according to Eq. (3):

BitDepth=8+sps_bitdepth_minus8   Eq. (2)

QpBdOffset=6×ps_bitdepth_minus8   Eq. (3)

In some examples, the GCI bit (1601) equal to 1 specifies that thesyntax element (1701) for all pictures in a scope for an output layerset (OlsInScope) may be equal to 0. The GCI bit (1601) equal to 0 doesnot impose such a constraint. Thus, the GCI bit (1601) equal to 1 canspecify no use of the extended dynamic range coding tool in the codingof the bitstream.

In some embodiments, the GCI bit (1602) and the syntax element (1702)are used to provide, in different scopes, control of a coding tool of aslice based Rice coding for residual coding in the transform skip mode,such as a slice based Rice parameter selection for residual coding inthe transform skip mode.

According to an aspect of the disclosure, a slice based Rice parameterselection for transform skip residual coding can be included in a rangeextension of a video standard. In some examples, one control flag (e.g.,denoted by sps_ts_residual_coding_rice_present_in_sh_flag, syntaxelement (1702)) is signaled in a sequence parameter set (SPS) whentransform skip mode is enabled (e.g., syntax elementsps_tranform_skip_enabled_flag is true) to indicate the signaling ofRice parameter for the transform skip slices is enabled or disabled,such as shown in FIG. 17 .

When the control flag is signaled as enabled (e.g., equal to “1”), onesyntax element (e.g., denoted by sh_ts_residual_coding_rice_idx_minus1)is further signaled for each transform skip slice, for example in theslice header, to indicate a selection of the Rice parameter of thattransform skip slice. When the control flag is signaled as disabled(e.g. equal to “0”), no further syntax element is signaled at slicelevel (e.g., slice header) to indicate the Rice parameter selection forthe transform skip slice and a default Rice parameter may be used forall the transform skip slices in coded video data that refers to the SPSin an example.

For example, the syntax element (1702) equal to 1 in an SPS specifiesthat a slice header flag denoted bysh_ts_residual_coding_rice_idx_minus1 may be present in slice header(e.g., slice header( )) syntax structures of slices that refer to theSPS. The syntax element (1702) equal to 0 in an SPS specifies that theslice header flag sh_ts_residual_coding_rice_idx_minus1 is not presentin slice header( ) syntax structures of slices referring to the SPS.When not present, the value ofsps_ts_residual_coding_rice_present_in_sh_flag is inferred to be equalto 0 in some examples.

In some examples, syntax element can be included in general constraintinformation to control, in a scope of an output layer set, the use ofthe coding tool of a slice based Rice coding for residual coding in thetransform skip mode. For example, the syntax element (1602) equal to 1specifies that the syntax element (1702) for all pictures in a scope foran output layer set (OlsInScope) may be equal to 0. The syntax element(1602) equal to 0 does not impose such a constraint. Thus, in someexamples, the GCI bit (1602) equal to 1 in a bitstream can specify nouse of the slice based Rice parameter selection for transform skipresidual coding for coding the bitstream.

In some embodiments, the GCI bit (1603) and the syntax element (1703)are used to provide, in different scopes, control of one or more codingtools for Rice parameter derivation for the binarization of some syntaxelements, such as abs_ remainder[ ] and dec_abs_level[ ] and the like inthe regular residual coding (RRC). In some examples, the regularresidual coding (RRC) refers to some techniques for coding blocks thatare obtained by transform and quantization. In some examples, the RRCcan be modified for blocks that are obtained by quantization only. Insome examples, transform skip residual coding (TSRC) refers to sometechniques that are dedicated for coding blocks that are obtainedbypassing transform (also referred to as transform skip).

In some examples, a video coding standard may include one or more codingtools for Rice parameter derivation for the binarization of some syntaxelements, such as abs_remainder[ ] and dec_abs_level[ ], and a rangeextension of the video coding standard can include one or morealternative coding tools for Rice parameter derivation for thebinarization of some syntax elements, such as abs_remainder[ ] anddec_abs_level[ ].

In some examples, a video standard uses a local template based techniquefor Rice parameter derivation. For examples, a template that includesone or more (e.g., 5 in an example) neighboring coefficient levels isused for the rice parameter derivation. For example, a sum of absolutecoefficient values inside the template can be calculated, then the Riceparameter is determined based on the sum. In an example, a look up tablecan be used to determine the Rice parameter based on the sum.

It is noted that the Rice parameter can be determined by other suitablecoding tools. In an example, an equation can be used to determine theRice parameter based on the sum. In another example, context modelingcan be used to determine the Rice parameter based on statistics ofneighboring coefficient levels. In some examples, the range extension ofthe video standard can specify one or more alternative coding tools forthe Rice parameter derivation.

In some examples, the range extension of the video standard can includemodifications to the RRC for use in other scenarios. In an example, therange extension can include a different context modeling tool and aresidual signal rotation tool for residual coding in the transform skipmode.

In some examples, the syntax element (1703) in an SPS equal to 1specifies that an alternative Rice parameter derivation (e.g., analternative coding tool for Rice parameter derivation in the rangeextension) for the binarization of abs_remainder[ ] and dec_abs_level[ ]is used for coding a CLVS that refers to the SPS. The syntax element(1703) equal to 0 specifies that the alternative Rice parameterderivation for the binarization of abs_remainder[ ] and dec_abs_level[ ]is not used for coding the CLVS that refers to the SPS. When notpresent, the value of syntax element (1703) is inferred to be equal to0.

In some examples, the syntax element (1603) equal to 1 specifies thatsyntax element (1703) for all pictures in a scope of an output layer set(OlsInScope) may be equal to 0. The syntax element (1603) equal to 0does not impose such a constraint. Thus, in some examples, the GCI bit(1603) equal to 1 can specify no use of the alternative Rice parameterderivation (e.g., an alternative coding tool for Rice parameterderivation specified in the range extension specified) for thebinarization of abs_remainder[ ] and dec_abs_level[ ] for coding thebitstream.

In some embodiments, the GCI bit (1604) and the syntax element (1704)are used to provide, in different scopes, control of statistics basedRice parameter derivation for the binarization of abs_remainder[ ] anddec_abs_level[ ].

According to an aspect of the disclosure, Rice parameter derivation forthe binarization of abs_remainder[ ] and dec_abs_level[ ] can beinitialized at a start of each transform unit (TU) using statisticsaccumulated from previous TUs. In some examples, the statistics basedRice parameter derivation can be included in a range extension of avideo standard.

In some examples, a control flag e.g., the syntax element (1704) denotedby sps_persistent_rice_adaptation_enabled_flag in an SPS is used tocontrol the statistics based Rice parameter derivation. For example, thesyntax element (1704) equal to 1 in an SPS specifies that Rice parameterderivation for the binarization of abs_remainder[ ] and dec_abs_level[ ]is initialized at the start of each TU using statistics accumulated fromprevious TUs. The syntax element (1704) equal to 0 specifies that noprevious TU state is used in Rice parameter derivation of the currentTU. When not present, the value of the syntax (1704) is inferred to beequal to 0.

Further, in an embodiment, the syntax element (1604) equal to 1specifies that syntax element (1704) for all pictures in a scope for anoutput layer set (OlsInScope) may be equal to 0. The syntax element(1604) equal to 0 does not impose such a constraint. Thus, in someexamples, the GCI bit (1604) equal to 1 can specify no use of thestatistics based Rice parameter derivation for coding the bitstream.

In some embodiments, the GCI bit (1605) and the syntax element (1705)are used to provide, at different scopes, control of a coding tool thatis used to code a position of a last significant coefficient during anentropy coding of transform coefficients. In an example, the position ofthe last significant coefficient can be coded by different coding tools.For example, a video standard may specify a first coding tool that candetermine the position of the last significant coefficient by coding twocoordinates of the position denoted by LastSignificantCoeffX andLastSignificantCoeffY variables (e.g., coded relative to (0,0) for eachtransform block); and a range extension of the video standard canspecify alternative coding tool, such as a second coding tool that candetermine the position of the last significant coefficient by codingrelative coordinates of the last significant coefficient with referenceto a bottom right corner of a transform block in an example.

In some examples, the syntax element (1705) equal to 1 in an SPSspecifies that a slice header flag (slice scope) denoted bysh_reverse_last_sig_coeff_flag is present in slice header syntaxstructures (e.g., slice_header( ) in some examples) that refer to theSPS. The syntax element (1705) equal to 0 in an SPS specifies that theslice header flag sh_reverse_last_sig_coeff_flag is not present in theslice header syntax structures that refer to the SPS, and the sliceheader flag sh_reverse_last_sig_coeff_flag may be inferred to be zero.When not present, the value of syntax element (1705) is inferred to beequal to 0.

In some examples, the value of the slice header flagsh_reverse_last_sig_coeff_flag of a slice is used to determine theposition derivation of the last significant coefficient in transformcoefficients in the scaling and transformation processes in the codingof the slice. In an example, when sh_reverse_last_sig_coeff_flag isequal to 1 for a slice, in the slice, the last significant coefficientposition can be coded by the alternative coding tool in the rangeextension of the video standard, such as the second coding tool that candetermine the position of the last significant coefficient by codingrelative coordinates of the last significant coefficient with referenceto a bottom right corner of a transform block in an example. Otherwise(e.g., sh_reverse_last_sig_coeff_flag is equal to 0 for a slice), in theslice, the current coordinates (e.g., coded relative to (0,0) for eachtransform block) for the last significant coefficient position are codedby the first coding tool.

In some examples, the GCI bit (1605) equal to 1 specifies that thesyntax element (1705) for all pictures in a scope for an output layerset (OlsInScope) may be equal to 0. The GCI bit (1605) equal to 0 doesnot impose such a constraint. Thus, the GCI bit (1605) equal to 1 canspecify no use of the second coding tool in the position derivation ofthe last significant coefficient for the scope of the bitstream.

FIG. 18 shows a flow chart outlining a process (1800) according to anembodiment of the disclosure. The process (1800) can be used in a videodecoder. In various embodiments, the process (1800) are executed byprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video decoder (410), the processing circuitrythat performs functions of the video decoder (510), and the like. Insome embodiments, the process (1800) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1800). Theprocess starts at (S1801) and proceeds to (S1810).

At (S1810), a value of a first syntax element (e.g.,general_no_reverse_last_sig_coeff_constraint_flag) for coding control ina first scope of coded video data (e.g., an output layer set) in abitstream is determined. The first syntax element is associated with acoding tool for coding a position of a last significant coefficientduring an entropy coding of transform coefficients, such as analternative tool in the range extension (e.g., the second coding toolthat can determine the position of the last significant coefficient bycoding relative coordinates of the last significant coefficient withreference to a bottom right corner of a transform block in an example).

In an example, the first syntax element is decoded from a syntaxstructure for general constraint information in response to a syntaxelement (e.g., gci_num_additional_bits) in the syntax structureindicating additional bits for general constraint information in thesyntax structure.

At (S1820), when the value of the first syntax element is a first value,the process proceeds to (1830); otherwise, the process proceeds to(S1840). The first value is indicative of disabling of the coding toolin the coding of the first scope of coded video data in the bitstreamthat includes one or more second scopes of coded video data (e.g., oneor more CLVS in the output layer set).

In some examples, the first syntax element is in general constraintinformation for coding control of pictures in an output layer set outputat the decoder. In an example, the first value of the first syntaxelement is indicative of disabling the coding tool in each coded layervideo sequence (CLVS) in the output layer set.

At (S1830), in response to the first syntax element being the firstvalue, the first scope of coded video data in the bitstream is decodedwithout invoking the coding tool.

In some examples, a second syntax element (e.g.,sps_reverse_last_sig_coeff_enabled_flag) for coding control of a codedlayer video sequence (CLVS) in the bitstream is constrained to have avalue indicative of no invoking of the coding tool for decoding theCLVS. In an example, the value of the second syntax element indicates anonexistence of a slice header flag associated with the coding tool in aslice header of a slice in a picture of the CLVS.

At (S1840), in response to the first syntax element being a secondvalue, a value of a second syntax element (e.g.,sps_reverse_last_sig_coeff_enabled_flag) for coding control of a secondscope of coded video data, such as coded layer video sequence (CLVS), inthe bitstream is determined for decoding of the coded video data in thesecond scope. The second syntax element is indicative of anenabling/disabling of the coding tool in the CLVS. In an example, thesecond syntax element is not presented in a sequence parameter set (SPS)for the CLVS, the value of the second syntax element is inferred forindicating disabling of the coding tool in the CLVS.

In some examples, in response to the value of the second syntax elementindicative of an enabling of the coding tool in the CLVS, a slice headerflag (e.g., sh_reverse_last_sig_coeff_flag) in a slice header of a sliceis determined, for example decoded from the slice header of the slice.The slice header flag is indicative of a use/no use of the coding toolfor coding the slice.

The process (1800) can be suitably adapted. Step(s) in the process(1800) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used.

FIG. 19 shows a flow chart outlining a process (1900) according to anembodiment of the disclosure. The process (1900) can be used in a videoencoder. In various embodiments, the process (1900) is executed byprocessing circuitry, such as the processing circuitry in the terminaldevices (310), (320), (330) and (340), the processing circuitry thatperforms functions of the video encoder (403), the processing circuitrythat performs functions of the video encoder (603), the processingcircuitry that performs functions of the video encoder (703), and thelike. In some embodiments, the process (1900) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1900). Theprocess starts at (S1901) and proceeds to (S1910).

At (S1910), the processing circuitry determines whether a coding tool isused during encoding of a first scope (e.g., an output layer set) ofcoded video data in a bitstream. The coding tool is associated withcoding a position of a last significant coefficient during an entropycoding of transform coefficients. For example, the coding tool is analternative coding tool in the range extension, such as the secondcoding tool that can derive the position of the last significantcoefficient in a transform block by coding relative coordinates of thelast significant coefficient with reference to a bottom right corner ofthe transform block. The first scope of coded video data includes one ormore second scopes (e.g., CLVSs) of coded video data.

In some examples, the processing circuitry can determine whether thecoding tool is used based on second syntax elements (e.g.,sps_reverse_last_sig_coeff_enabled_flag) for coding control of codedlayer video sequences (CLVSs) in the bitstream. In some examples, theprocessing circuitry can determine whether the coding tool is used basedon slice header flags (e.g., sh_reverse_last_sig_coeff_flag) in sliceheaders of slices that are encoded. A slice header flag ((e.g.,sh_reverse_last_sig_coeff_flag) of a slice is indicative of a use/no useof the coding tool for coding a slice.

At (S1920), when the coding tool is not used in the coding of the firstscope of coded video data, the process proceeds to (S1930); otherwise,the process proceeds to (S1940).

At (S1930), a first syntax element (e.g., generalno_reverse_last_sig_coeff_constraint_flag) having a first value isencoded in the bitstream. The first syntax element is for coding controlin the first scope of coded video data (e.g., an output layer set) inthe bitstream. The first syntax element is associated with the codingtool for coding a position of a last significant coefficient during anentropy coding of transform coefficients. The first value indicates a nouse of the coding tool in the coding of the first scope of coded videodata.

In an example, the first syntax element is encoded in a syntax structurefor general constraint information, and a syntax element (e.g.,gci_num_additional_bits) in the syntax structure is adjusted to indicateadditional bits for general constraint information in the syntaxstructure.

At (S1940), the first syntax element having a second value is encoded inthe bitstream. In some examples, the first syntax element is not encodedin the bitstream, for example, in the case the second value is thedefault value for the first syntax element, and then (S1940) can beskipped.

The process (1900) can be suitably adapted. Step(s) in the process(1900) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used.

The techniques described above (e.g., the techniques for signalingconstraints flags, adaptive resolution parameters, and/or the like) canbe implemented as computer software using computer-readable instructionsand physically stored in one or more computer-readable media. Forexample, FIG. 20 shows a computer system (2000) suitable forimplementing certain embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 20 for computer system (2000) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2000).

Computer system (2000) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2001), mouse (2002), trackpad (2003), touchscreen (2010), data-glove (not shown), joystick (2005), microphone(2006), scanner (2007), camera (2008).

Computer system (2000) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2010), data-glove (not shown), or joystick (2005), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2009), headphones(not depicted)), visual output devices (such as screens (2010) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2000) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2020) with CD/DVD or the like media (2021), thumb-drive (2022),removable hard drive or solid state drive (2023), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2000) can also include an interface (2054) to one ormore communication networks (2055). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (2049) (such as,for example USB ports of the computer system (2000)); others arecommonly integrated into the core of the computer system (2000) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (2000) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2040) of thecomputer system (2000).

The core (2040) can include one or more Central Processing Units (CPU)(2041), Graphics Processing Units (GPU) (2042), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2043), hardware accelerators for certain tasks (2044), graphicsadapters (2050), and so forth. These devices, along with Read-onlymemory (ROM) (2045), Random-access memory (2046), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(2047), may be connected through a system bus (2048). In some computersystems, the system bus (2048) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (2048), or through a peripheral bus (2049). In anexample, the screen (2010) can be connected to the graphics adapter(2050). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (2041), GPUs (2042), FPGAs (2043), and accelerators (2044) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2045) or RAM (2046). Transitional data can be also be stored in RAM(2046), whereas permanent data can be stored for example, in theinternal mass storage (2047). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2041), GPU (2042), massstorage (2047), ROM (2045), RAM (2046), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (2000), and specifically the core (2040) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (2040) that are of non-transitorynature, such as core-internal mass storage (2047) or ROM (2045). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2040). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2040) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2046) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2044)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding in a decoder,comprising: determining, by a processor, a first syntax element forcoding control in a first scope of coded video data in a bitstream, thefirst syntax element being associated with a coding tool for coding aposition of a last significant coefficient during an entropy coding oftransform coefficients; and in response to the first syntax elementbeing a first value indicative of disabling of the coding tool in thefirst scope, decoding, by the processor, the first scope of coded videodata in the bitstream that includes one or more second scopes of codedvideo data without invoking the coding tool.
 2. The method of claim 1,wherein the first syntax element is denoted bygeneral_no_reverse_last_sig_coeff_constraint_flag in general constraintinformation for coding control of pictures in an output layer set at thedecoder, and the coding tool codes a position of a last significantcoefficient in a transform block relative to a bottom right corner ofthe transform block.
 3. The method of claim 2, wherein the first valueof the first syntax element is indicative of disabling the coding toolin each coded layer video sequence (CLVS) in the output layer set. 4.The method of claim 2, further comprising: constraining a second syntaxelement for coding control of a coded layer video sequence (CLVS) in thebitstream to have a value indicative of no invoking of the coding toolfor decoding the CLVS.
 5. The method of claim 4, wherein the value ofthe second syntax element indicates a nonexistence of a slice headerflag associated with the coding tool in a slice header of a slice in apicture of the CLVS.
 6. The method of claim 2, further comprising: inresponse to the first syntax element being a second value, determining avalue of a second syntax element for coding control of a coded layervideo sequence (CLVS) in the bitstream, the second syntax element beingindicative of an enabling/disabling of the coding tool in the CLVS. 7.The method of claim 6, further comprising: in response to the value ofthe second syntax element indicative of an enabling of the coding toolin the CLVS, decoding a slice header flag in a slice header of a slice,the slice header flag being indicative of a use/no use of the codingtool for coding the slice.
 8. The method of claim 6, wherein thedetermining the value of the second syntax element further comprises:inferring, in response to the second syntax element not presenting in asequence parameter set (SPS) for the CLVS, the value of the secondsyntax element for indicating a disable of the coding tool in the CLVS.9. The method of claim 1, wherein the determining the first syntaxelement further comprises: decoding the first syntax element from asyntax structure for general constraint information in response to asyntax element in the syntax structure indicating additional bits forgeneral constraint information in the syntax structure.
 10. An apparatusfor video decoding, comprising processing circuitry configured to:determine a first syntax element for coding control in a first scope ofcoded video data in a bitstream, the first syntax element beingassociated with a coding tool for coding a position of a lastsignificant coefficient during an entropy coding of transformcoefficients; and in response to the first syntax element being a firstvalue indicative of no use of the coding tool in the first scope, decodethe first scope of coded video data in the bitstream that includes oneor more second scopes of coded video data without invoking the codingtool.
 11. The apparatus of claim 10, wherein the first syntax element isdenoted by general_no_reverse_last_sig_coeff_constraint_flag in generalconstraint information for coding control of pictures in an output layerset, and the coding tool codes a position of a last significantcoefficient in a transform block relative to a bottom right corner ofthe transform block.
 12. The apparatus of claim 11, wherein the firstvalue of the first syntax element is indicative of disabling the codingtool in each coded layer video sequence (CLVS) in the output layer set.13. The apparatus of claim 11, wherein the processing circuitry isconfigured to: constrain a second syntax element for coding control of acoded layer video sequence (CLVS) in the bitstream to have a valueindicative of no invoking of the coding tool for decoding the CLVS. 14.The apparatus of claim 13, wherein the value of the second syntaxelement indicates a nonexistence of a slice header flag associated withthe coding tool in a slice header of a slice in a picture of the CLVS.15. The apparatus of claim 11, wherein the processing circuitry isconfigured to: in response to the first syntax element being a secondvalue, determine a value of a second syntax element for coding controlof a coded layer video sequence (CLVS) in the bitstream, the secondsyntax element being indicative of an enabling/disabling of the codingtool in the CLVS.
 16. The apparatus of claim 15, wherein the processingcircuitry is configured to: in response to the value of the secondsyntax element indicative of an enabling of the coding tool in the CLVS,decode a slice header flag in a slice header of a slice, the sliceheader flag being indicative of a use/no use of the coding tool forcoding the slice.
 17. The apparatus of claim 15, wherein the processingcircuitry is configured to: infer, in response to the second syntaxelement not presenting in a sequence parameter set (SPS) for the CLVS,the value of the second syntax element for indicating a disable of thecoding tool in the CLVS.
 18. The apparatus of claim 10, wherein theprocessing circuitry is configured to: decode the first syntax elementfrom a syntax structure for general constraint information in responseto a syntax element in the syntax structure indicating additional bitsfor general constraint information in the syntax structure.
 19. Anon-transitory computer-readable storage medium storing instructionswhich when executed by at least one processor cause the at least oneprocessor to perform: determining a first syntax element for codingcontrol in a first scope of coded video data in a bitstream, the firstsyntax element being associated with a coding tool for coding a positionof a last significant coefficient during an entropy coding of transformcoefficients; and in response to the first syntax element being a firstvalue indicative of no use of the coding tool in the first scope,decoding the first scope of coded video data in the bitstream thatincludes one or more second scopes of coded video data without invokingthe coding tool.
 20. The non-transitory computer-readable storage mediumof claim 19, wherein the first syntax element is denoted by generalno_reverse_last_sig_coeff_constraint_flag in general constraintinformation for coding control of pictures in an output layer set, thecoding tool codes a position of a last significant coefficient in atransform block relative to a bottom right corner of the transformblock, and the first value of the first syntax element is indicative ofdisabling the coding tool in each coded layer video sequence (CLVS) inthe output layer set.